Coated ballistic structures

ABSTRACT

Armor components having a ceramic substrate, a thermal sprayed barrier coating covering the substrate material to form a barrier coated substrate, and an outermost encapsulation of metal generally surrounding at least the periphery of the barrier coated substrate are disclosed herein. The encapsulation of metal was cast to the ceramic substrate as molten metal, and the thermal sprayed barrier coating comprises a cermet material, a ceramic material, or a combination thereof. The ceramic substrate is preferably a ceramic tile for ballistic armor. Also disclosed are armor components having a plurality of the ceramic tiles interconnected by the encapsulation of metal, with the metal, which was casted thereto, surrounding at least the periphery of each of the plurality of the armor components.

RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.14/031,070, filed Sep. 19, 2013, which claims the benefit of U.S.Provisional Application No. 61/702,772, filed Sep. 19, 2012, which isincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to ballistic structures such astiles, plates, or armor whether for a person, vehicle, or aircraft and,more particularly, to a coated ballistic structure capable ofencapsulation in a molten metal.

BACKGROUND

Desired armor protection levels can usually be obtained if weight is nota consideration. However, in many armor applications, there is a premiumput on lightweight armor. Some areas of application where lightweightarmor are important include ground combat and tactical vehicles,portable hardened shelters, helicopters, and various other aircraft usedby the Army and the other Services. Another example of an armorapplication in need of reduced weight is personnel body armor worn bysoldiers and law enforcement personnel.

There are two prevalent hard passive armor technologies in general use.The first and most traditional approach makes use of metals such asarmor grade steel. The second approach uses ceramics. Each material hascertain advantages and limitations. Broadly speaking, metals are moreductile and are generally superior at withstanding multiple hits.However, they typically have a large weight penalty and are not asefficient at stopping armor-piercing threats. Ceramics areextraordinarily hard, strong in compression, lighter weight, andbrittle, making them efficient at eroding and shattering armor-piercingthreats, but not as effective at withstanding multiple hits.

Attempts to take advantage of the best characteristics of the metal andthe ceramic have been tried. For example, ceramic tiles have beenencapsulated in a metal framework using a hot-press process followed byextensive grinding and finishing to produce an acceptable armor article.The grinding and finishing (post-processing) steps are expensive andtime consuming processes. Moreover, additional processing is required tobuild the metal matrix or frame that connects multiple ceramic tiles.The metal frame is typically a piece of solid steel precision machinedto create openings that mirror the tile dimensions or is slightlyundersized then heated and the tiles are shrink fit into the matrix.Metal plates are then added to both the front and back of the metalframe and super-plastically bonded to the metal frame, thus totallyencapsulating the tiles. This process is lengthy and costly.

One such method of encasing ceramic tiles in a metal frame is disclosedin U.S. Pat. No. 5,686,689 to Snedeker, et al. Ceramic tiles were placedinto individual cells of a metallic frame consisting of a backing plateand thin surrounding walls. A metallic cover was then welded over eachcell, encasing the ceramic tiles. A benefit to encasing the ceramic tileis that once fractured pieces cannot move away easily and a degree ofprotection is maintained in the area of the ceramic tile.

Substantial development efforts are ongoing with metal encapsulatedceramic tiles or plates to find more cost-effective and fasterproduction methods that utilize the advantages of both materials tomaintain or lower the armor's weight and to decrease the negativeeffects of fractured tiles such as reduced penetration resistance anddamage to neighboring tiles, while also improving the ceramic'sintegrity during the metal encapsulation process.

SUMMARY

Durable ceramic and metallic coatings applied to ceramic substrates ofvarious shapes and sizes suitable for ballistic and/or armorapplications are disclosed herein that protect the tiles whileundergoing a molten metal casting operation. The ceramic and metalliccoatings are preferably plasma sprayed coating that include a ceramictop coat layer of aluminum oxide, zirconium oxide, or other oxides withor without a metallic bond coat layer. This coating protects theunderlying ceramic tile, which is composed of boron carbide, siliconcarbide, alumina (Al₂O₃) or other type of hard ceramic, from reactingchemically with the molten metal. Molten metal is cast around theceramic tiles to create a lattice of ceramic tiles that are used forprotection from projectiles and shrapnel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a hexagonally-shaped tile.

FIG. 2 is a cross-sectional view of the tile of FIG. 1 taken along line2-2.

FIG. 3 is partial cut-way top plan view of an armor member that includesthe tiles of FIG. 1.

FIGS. 4A-4E are illustrations of alternate exemplary shapes for an armortile.

FIG. 5A is a photograph of one embodiment of an armor member havingseven tiles encapsulated in metal.

FIG. 5B is an illustration of one arrangement of seven tilesencapsulated within the armor member of FIG. 5A.

FIG. 6 is an illustration of the armor member of FIG. 5A taken alongline 6-6.

FIGS. 7A and 7B are photographs of a primary mold to make a foam patternto make the armor member of FIG. 5A.

FIG. 8 is an image of one embodiment of a foam pattern that results fromthe molds in FIGS. 7A-7B.

FIG. 9 is a photograph of a ceramic secondary mold surrounding a foampattern like that of FIG. 8.

DETAILED DESCRIPTION

The following detailed description will illustrate the generalprinciples of the invention, examples of which are additionallyillustrated in the accompanying drawings. In the drawings, likereference numbers indicate identical or functionally similar elements.

Armor components disclosed herein provide the ability for ceramic tilesto be successfully encapsulated in metal via a casting process utilizingmolten metal to form an armor member. The armor member and the method ofmaking the same do not chemically degrade or crack the ceramic tiles orthe surrounding steel. The armor components comprise a ceramic substrateor other similar hard substrate suitable for ballistic and/or armorapplications coated with a material that protects the underlying ceramictile from chemical and thermal interactions with the molten metal duringthe casting process. The coating on the tiles also minimizes stresses,coating spallation, and delamination caused by the molten metal and/orby the solidifying metal (including the change in stresses when themetal changes from molten to solid).

One challenge is to cast the molten metal (for example, steel) aroundthe tile without cracking the tile. The mismatch in the coefficient ofthermal expansion (“CTE”) of the tile relative to the metal causesrelatively high thermal loading and strain in both the tile and thesurrounding metal, which may both crack. To adequately address the CTEmismatch, reduce processing risk, and improve the ballistic performance,a coating, in particular a thermal sprayed coating such as a plasmasprayed coating, a flamed coating, or any variation of a thermalcoating, is applied to the tile. In one embodiment, the coating isapplied to a SiC or Al₂O₃ ceramic tile, which is then cast into a steelmatrix.

FIG. 1 is a top view of an armor component 10 that includes a tile 12having a perimeter 13 and a coating 14 on both primary faces and theperimeter of the tile. In other words, the tile is essentially,completely surrounded by the coating 14 as shown in the cross-section inFIG. 2. While the tile 12 illustrated in FIG. 1 is hexagonal in shape,there is no limit to the shape of the tile or plates to be coated bycoating 14. Moreover, the armor component 10 may also be a plate, panel,or other substrate for ballistic, defense, and/or armor applicationssuch as those for the body, vehicle, aircraft, etc. The word “tile” asused herein is meant to be and include other forms of ballistic,defense, and/or armor substrates, including plates, panels, and thelike.

As seen in FIGS. 4A-4E, the tiles or plates may have any number ofalternate shapes and again are not limited to those illustrated herein.In the embodiment in FIG. 4A, the tile or plate may be a circular shapedtile 15. FIG. 4B shows a triangular tile 16, FIG. 4C shows aquadrilateral tile 18, FIG. 4D shows a pentagonal tile 20, and FIG. 4Eshows a hexagonal tile 22. The shapes shown in FIGS. 1 and 4A-4D are byway of example only. Other polygonal shapes may be used. In addition,the shape of the tile need not be a regular geometric shape. The tilemay have any shape needed for a particular application.

The core of the armor component 10, as mentioned above, is preferably atile 12 or plate of or including a ceramic material selected from thegroup consisting of aluminum oxide, silicon carbide, boron carbide,titanium diboride, aluminum nitride, silicon nitride and tungstencarbide. Tile 12 may also be made of any hard, high compressive strengthmaterial having a Vickers hardness of about 12 GPa or greater and acompressive strength of about 2 GPa or greater.

The material for the coating 14 may be, but is not limited to, aplasma-sprayable ceramic or cermet material such as aluminum oxide,magnesium aluminate spinel, zirconium oxide, other oxides, andcombinations thereof. “Cermet” means a material comprising a metal or ametal alloy and a ceramic powder or a mixture of ceramic powders. Cermetis fabricated from the ceramic powder selected from a group of compoundsrepresented and exemplified by the titanium-aluminum oxide system. Othersystems, such as and including zirconium, hafnium, beryllium, vanadiumoxides, nitrates, silicates or borides, etc., in combination with ametal, such as titanium, aluminum, magnesium, nickel, lithium, calcium,or their alloys are equally suitable for fabrication of cermets of theinvention. In addition to these named systems, any other suitable alloysystem meeting the general conditions for processing of the cermets mayalso be advantageously used to fabricate these cermets using themolten-metal-infiltration method and process and are intended to bewithin the scope of the invention. In one embodiment, the cermet may bea mixture of a ceramic, such as for example, aluminum oxide, zirconiumoxide, hafnium oxide, beryllium oxide, vanadium oxide, boron carbide,aluminum nitride, zirconium nitride, hafnium nitride, vanadium nitride,aluminum boride, zirconium boride, hafnium boride, vanadium boride,aluminum silicate, zirconium silicate, hafnium silicate, vanadiumsilicate powders or their mixtures, in combination with a metal such astitanium, aluminum, magnesium, nickel, lithium, calcium, or othersuitable metals, or their alloys, etc.

These materials may be provided as a powder for use in plasma spraying.The powder may have an average particle size of about 5 μm to about 120μm, preferably about 10 μm to about 50 μm.

The coating 14, which forms a layer on the tile 12 as illustrated inFIG. 2, may be plasma sprayed onto the tile 12 or other armor component10 at a thickness of about 0.001 to about 0.125 inches thick. In oneembodiment, the coating 14 is about 0.002 to about 0.005 inches thick.

In one embodiment, the coating 14 may be a functionally graded coatingapplied to tile 12 where the surface coating CTE will match that of thetile surface and functionally change as one moves further from the tilesurface. The outer or exposed part of the coating will ultimately matchthe surrounding metal matrix CTE (metal that is poured to encapsulatethe tiles). When the metal is investment cast around the tiles andbegins to solidify, the stresses will be reduced on the metal matrix andthe tile surface as the CTE mismatch is minimized. An important featureof these coatings is their ability to form a barrier layer between thetile and the molten metal to eliminate degradation of the tiles whetherchemical or mechanical.

As shown in FIG. 2, the armor component 10 may also include an optionalmetallic bond coating 19 that defines a layer external to the coating 14to enhance the armor component's adhesion/bond to molten metal during acasting process. The metallic bond coating 19 may be an additionalplasma spray coating.

The optional metallic bond coating 19 may be a metal or metal alloylayer applied to coating 14. The metal or metal alloy may be a powderfor thermal spray applications such that the bond coat may be providedas a plasma spray coating. The metallic bond coating 19 may be appliedat a thickness of about 0.002 to about 0.004 inches. In one embodiment,the metallic bond coating 19 is about 0.003 inches thick. The metal ormetal alloy may be a powder, for example, but not limited to, analuminum, cobalt, copper, iron, molybdenum, nickel metal or metalalloys.

Referring now to FIG. 3, another aspect of the invention is an armormember 30 comprising a metal encapsulate 32 and at least one tile arraylayer 34 encapsulated by the metal. The tile array layer 34 is comprisedof a plurality of armor components 10 wherein each armor component 10comprises a tile or plate having a coating 14, as discussed above. Thematerials of construction, shapes and features of the armor components10 used in the armor member 30 are as discussed previously. The tilearray layer 30 may be comprised of a variety of shapes of components 10.The important feature is that the tile array layers provide as muchcoverage as possible for the intended item to be protected whether avehicle, airplane, building, or person. To this end, various regular andirregular shapes may be combined within a single layer to obtain as muchcoverage as possible. While hexagonal-shaped tiles 12 are shown in FIG.3, the methods of arranging the components 10 to provide maximumcoverage of the underlying body to which the armor member 30 may beattached are applicable to any shape of tile.

In another embodiment, the photograph of FIG. 5, armor member 40includes seven tiles 12 having coating 14 which are encased in solidmetal 46. This embodiment includes seven tiles in an arrangement where,as depicted in FIG. 5B, a first tile 48 is designated as the centraltile 48′ and the remaining six tiles 49 are arranged equally distantabout the central tile and equally distant apart from one another. Inone embodiment, the tiles are spaced apart about 1/16 inch to about oneinch, and preferably are spaced apart about ⅛ inch from all adjacentsides of neighboring tiles. As seen in FIG. 5A and FIG. 6, the armormember may include sides 60 of metal defining the central portion of theexterior perimeter of the armor member and ridges 62, which are thickerthan the sides and are disposed over all the seams between the tiles 12and along the upper and lower outer perimeter of the armor member (i.e.,above and below the sides 60). Extending from the ridges 62 onto outermajor surfaces of the tiles 12 (the front and back faces of the tiles12) are flanges 64, which define holes 66 exposing the center of thefront and back faces of the tiles. In another embodiment, the metal maycompletely cover the front and back faces of the tiles 12 such that noflanges 64 are present. The armor members 30 and 40 may be cast usingfoam pattern technology as explained below.

One method of encapsulating one or more tiles 12 in molten metal is aninvestment casting technology called foam pattern technology (“FOPAT”).Foam pattern casting is advantageous over the lost-wax method forcasting an array of armor components because it is more rigid anddimensionally more stable. FOPAT uses various polymers in combinationwith a modified reaction injection molding process and alternate toolingmethods to produce investment casting patterns. The reaction injectionmolding is a polymer fabrication technique involving the extremely rapidimpingement mixing of two chemically reactive liquid streams that areinjected into a mold, resulting in simultaneous polymerization,cross-linking, and formation of the desired shape. FIGS. 7A-7B arephotographs of one example of a primary mold 52 for making a foampattern to encapsulate a seven tile configuration such as that shown inFIG. 5B to produce the armor member in FIG. 5A. In FIG. 7A, seven tiles12 are disposed in the mold and await an overmold of foam material. Oncethe foam material is molded over the tiles 12, a foam pattern 54 results(FIG. 8) and is then removed from the primary mold 52.

Thereafter, the foam pattern 54 is invested in a mold, as inconventional investment mold production, for example, as shown in FIG.9, in a ceramic shell 56 to create a secondary mold 58. The ceramic mold58 may be made from a slurry of ceramic material, where the ceramicshell builds around the foam pattern 54 as it is repeatedly dipped inthe slurry. The ceramic shell 56 is then heated to a high temperature ina heat treatment furnace until the foam material defining the foamportion of the foam pattern 54 evaporates. During this heating step, theceramic shell 56 is sintered and becomes rigid. Once the foam materialis evaporated and the ceramic shell 56 is sintered, the second mold 58is defined as a result of the open cavity surrounding the tiles 12.Molten metal may then be poured into the second mold 58 to cast thearmor member 40 such as the one shown in FIG. 5A.

This process does not require a pattern removal step and eliminates theneed for an autoclave, which is used to melt and remove wax patterns.Instead, the foam material portion of the foam pattern is burned outduring the firing of the ceramic shell 56. Foam pattern technology, withits stronger patterns and unique flow characteristics, is ideal for thinand complex sections. Other benefits of the foam pattern technologyinclude essentially no pattern shrinkage (i.e., stable pattern yieldwith no shell cracking defects), stronger patterns (enable insertion ofthe ceramic tiles without pattern defects), stiffer patterns (improveshandling, which avoids creep issue experiences with wax molds), patternstorage and shipment without damage or distortion, cost savings(potentially 30% cheaper per pattern), minimal heating required (foamreaction occurs at room temperature), and reduced cost of injectiontooling since the foam is injected at lower pressures than wax.

In an alternate method, the foam pattern 54 may be suspended in a vesselthat is filled with compacted sand, which is then heated to evaporatethe foam material. Thereafter, molten metal may be poured into thevacancies left by the evaporated foam material to form an armor member.

What is claimed is:
 1. An armor component comprising: a ceramicsubstrate having a first coefficient of thermal expansion; a thermalsprayed barrier coating covering the substrate material to form abarrier coated substrate; and an outermost encapsulation of metalgenerally surrounding at least the periphery of the barrier coatedsubstrate; wherein the encapsulation of metal was casted thereon asmolten metal having a second coefficient of thermal expansion; whereinthe thermal sprayed barrier coating comprises: a first coating appliedto the ceramic substrate and comprising a cermet material, a ceramicmaterial, or a combination thereof having a coefficient of thermalexpansion most closely matching the first coefficient of thermalexpansion; and a second coating over the first coating, the secondcoating comprising a metallic material and having a coefficient ofthermal expansion most closely matching the second coefficient ofthermal expansion.
 2. The armor component of claim 1, wherein theceramic substrate includes one or more of aluminum oxide, siliconcarbide, boron carbide, titanium diboride, aluminum nitride, siliconnitride, or tungsten carbide.
 3. The armor component of claim 1, whereinthe thermal sprayed barrier coating is a plasma-sprayed barrier coating.4. The armor component of claim 1, wherein the thermal sprayed barriercoating has a coating thickness of about 0.001 to about 0.125 inches. 5.The armor component of claim 1, wherein the ceramic or cermet materialsin the first coating are selected from the group consisting of aluminumoxide, magnesium aluminate spinel, zirconium oxide, and combinationsthereof.
 6. The armor component of claim 1, wherein the ceramicsubstrate comprises a ceramic tile for ballistic armor.
 7. The armorcomponent of claim 1, comprising a plurality of the armor componentsinterconnected by the encapsulation of metal; wherein the metalsurrounds at least the periphery of each of the plurality of the armorcomponents.
 8. An armor component comprising: a ceramic substrate havinga first coefficient of thermal expansion; a thermal sprayed barriercoating covering the substrate material to form a barrier coatedsubstrate; and an outermost encapsulation of metal generally surroundingat least the periphery of the barrier coated substrate; wherein theencapsulation of metal was casted thereon as molten metal having asecond coefficient of thermal expansion; wherein the thermal sprayedbarrier coating is a functionally graded coating having an exposedsurface comprising a coefficient of thermal expansion more closelymatching the coefficient of thermal expansion of the molten metal and aninterior surface against the ceramic substrate that has a coefficient ofthermal expansion more closely matching the coefficient of thermalexpansion of the ceramic substrate.
 9. The armor component of claim 8,wherein the ceramic substrate includes one or more of aluminum oxide,silicon carbide, boron carbide, titanium diboride, aluminum nitride,silicon nitride, or tungsten carbide.
 10. The armor component of claim8, wherein the thermal sprayed barrier coating is a plasma-sprayedbarrier coating.
 11. The armor component of claim 8, wherein the thermalsprayed barrier coating has a coating thickness of about 0.001 to about0.125 inches.
 12. The armor component of claim 8, wherein the interiorsurface of the thermal sprayed barrier coating comprises as a majoritythereof a ceramic material, a cermet material, or a combination thereofselected from the group consisting of aluminum oxide, magnesiumaluminate spinel, zirconium oxide, and combinations thereof.
 13. Thearmor component of claim 8, wherein the ceramic substrate comprises aceramic tile for ballistic armor.
 14. The armor component of claim 8,comprising a plurality of the armor components interconnected by theencapsulation of metal; wherein the metal surrounds at least theperiphery of each of the plurality of the armor components.
 15. An armorcomponent comprising: a ceramic substrate; a thermal sprayed barriercoating covering the substrate material to form a barrier coatedsubstrate; and an outermost encapsulation of metal generally surroundingat least the periphery of the barrier coated substrate; wherein theencapsulation of metal was casted thereon as molten metal; wherein thethermal sprayed barrier coating comprises a cermet material, a ceramicmaterial, or a combination thereof.
 16. The armor component of claim 15,wherein the ceramic substrate includes one or more of aluminum oxide,silicon carbide, boron carbide, titanium diboride, aluminum nitride,silicon nitride, or tungsten carbide.
 17. The armor component of claim15, wherein the thermal sprayed barrier coating is a plasma-sprayedbarrier coating.
 18. The armor component of claim 15, wherein thethermal sprayed barrier coating has a coating thickness of about 0.001to about 0.125 inches.
 19. The armor component of claim 15, wherein thethermal sprayed barrier coating is a functionally graded coating havingan exposed surface comprising a first coefficient of thermal expansionmore closely matching the coefficient of thermal expansion of the moltenmetal and an interior surface against the ceramic substrate that has asecond coefficient of thermal expansion more closely matching thecoefficient of thermal expansion of the ceramic substrate.
 20. The armorcomponent of claim 19, wherein the exposed surface comprises a metallicbond coat applied to the thermal sprayed barrier coating that has thefirst coefficient of thermal expansion.